The Hartford, Conn., insurer closed a $6.9 billion acquisition of fellow insurer Coventry Health Care last May, and it said Thursday that deal was the main factor behind its growth in this year's first quarter.

Aetna Inc. is the nation's third-largest health insurer, and its medical enrollment swelled 24 percent in the quarter to 22.7 million people, compared to last year.

Coventry serves customers in two markets primed for growth. It administers Medicaid, the state and federally funded program that covers the needy and disabled people, and it offers Medicare Advantage plans. Those are subsidized versions of the federal government's Medicare program for the elderly and also disabled people.

The health care overhaul expanded Medicaid eligibility in several states starting this year. Medicare Advantage plans face funding cuts due to the overhaul, but retiring Baby Boomers are sparking enrollment growth in these plans, as are employers who are dropping their retiree health coverage.

Overall, Aetna earned $665.5 million, or $1.82 per share, in the quarter that ended March 31. That's up from $490.1 million, or $1.48 per share, a year earlier.

Adjusted earnings totaled $1.98 per share, not counting one-time items like a $92 million loss from the early retirement of some long-term debt and costs tied to the Coventry deal.